The use of duplex sonography in the diagnosis of renal artery stenosis.

Both direct and indirect duplex sonography (DS) permit the diagnosis of significant renal artery stenosis. The validity of direct DS, based on the detection of increases in the blood velocity in stenotic arteries, is affected by numerous factors (inappropriate examination conditions, presence of vascular variants). In the technique of indirect DS, renal artery stenosis is detected via changes in the hemodynamics of intrarenal vessels ('tardus-et-parvus' phenomenon). Various evaluation parameters (signal shape, acceleration time, acceleration index, resistance index, pulsatility index) have proven useful for signal analysis. The intraindividual comparison of the two sides is an important instrument of stenosis detection in indirect DS. In clinically selected populations of hypertensive patients, DS may be used as a method of stenosis screening. DS has proven its practical value as a follow-up method after angioplastic intervention. It remains to be shown in future investigations whether "functional' classification of the degree of stenosis on the basis of Doppler sonographic findings is feasible.